Effect of ozone anneals on YBa sub(2)Cu sub(3-x)Co sub(x)O sub(z) thin films

We report on the effect of 200-500C ozone anneals on the resistivity versus temperature (RT) and Raman spectra characteristics of YBa sub(2)Cu sub(3-x)Co sub(x)O sub(z) (Co-YBCO) thin films, with x identical with 0.3, 0.5, 0.75, and 1.0. Cold wall anneals are conducted at approx. 1 atm. of a flowing O sub(2)/O sub(3) mixture with approx. 2% O sub(3) by weight. The enhanced partial pressure of atomic oxygen, relative to canonical O sub(2) anneals, provided by ozone to the surface of Co-YBCO films, leads to enhanced oxygenation. This is demonstrated by the observation of an increase in T sub(c) (25K to 75K for x identical with 0.3, 0 to 38K for x identical with 0.5, and 0 to a T sub(c)(onset) of 19K for x identical with 0.75) and improvement in Raman spectra data following ozone anneals. This high degree of oxygenation is unstable under O sub(2) anneals at temperatures as low as 200C. We attribute this to the fact that the partial pressure of oxygen above well oxygenated Co-YBCO is greater than 1 atm. at approx. 200C. We will discuss the implication of these results for the stability and uniformity of SNS ramp edge Josephson junctions which employ Co-YBCO N-layers.